U.S. Pat. No. 6,066,377 discloses hoses. that consist of an inner layer (in contact with the braking air) and of an outer layer made of polyamide, nylon-11 or nylon-12, and between these layers are one or two layers of high-density polyethylene (HDPE) and possibly a polyester reinforcing braid. The HDPE must be radiation-crosslinked so that the tube has mechanical strength, in particular burst strength, and it must contain a functionalized polyolefin in order to create adhesion between the polyamide and the HDPE. Examples are not reproducible and result in random results. The mechanical properties of the HDPE are insufficient and weaken the tube.
Patent application FR 2 812 928 discloses layered tubing made of polyamide formed from outer and inner layers made of nylon-11 or nylon-12, with inner layers made of nylon-6 containing, by weight, 14% of a plasticizer (butylbenzenesulphonamide), 7% of residual caprolactam, 10% of maleic-anhydride-grafted EPDM elastomer and 5% of maleic-anhydride-grafted polyethylene. The nylon-6 and nylon-11 or nylon-12 layers are bonded together with a tie layer. The tie layer is preferably a nylon-6, 12 or an anhydride-modified polyolefin. The plasticizer and the residual caprolactam of the PA-6 layers exude and cause delamination of the layers and stiffening of the PA-6 layers. The hose no longer has sufficient mechanical properties. In addition, the nylon-6 has a much greater water uptake than PA-11 or PA-12 and therefore its mechanical properties are substantially degraded.
A polyamide alloy has now been found which optimizes the balance between the amount and type of lower cost polyolefins/modified polyolefins used in the polyamide alloy, and the strict performance standards of some of the regulated industries in which the alloy is used. The polyolefin phase of the invention has both soft and hard domains.